The present invention relates to turbomachines and, more particularly, to means for shaping or reshaping an edge of a blade generally associated with turbomachines.
Blade elements used in turbomachines generally have a complex geometrical configuration designed to provide a desired aerodynamic interaction of the blade with the fluid working medium which will contribute to the optimum cycle efficiency of the turbomachine. A typical blade may vary in stagger angle, chord length, camber angle and thickness from blade tip to blade root. Fabrication of such blades is likewise a complex task, especially the shaping of the leading edge of the blade whose profile is critical to achieving the maximum cycle efficiency of the turbomachine. The blade configuration causes the position of the leading edge relative to the blade root to vary three dimensionally from blade root to blade tip and a profiling tool must follow the twisting leading edge along the length of the blade.
While the leading edge may exhibit the desired profile immediately after original manufacture, the leading edge is subject to erosion and damage from impinging contact with the fluid medium and foreign objects ingested into the turbomachine during its life in a field environment. As a result of erosion and damage, the leading edge loses its most efficient aerodynamic contour and must periodically be reshaped or recontoured to maintain maximum cycle efficiency.
Prior art devices used to shape the leading edge of turbomachinery blades to a desired profile have been of several types. The completely automatic or programmed device in which the position of the leading edge of the blade with respect to the cutting or grinding tool is automatically controlled by electromechanical means pre-programmed to provide the proper engagement of the leading edge and the tool. These automatic devices are complicated and prohibitively expensive. Scrapers, which are essentially manually operated tools configured specifically for shaping the leading edge of single blade configurations, are by their manual nature not suitable for precise, consistent and repeatable leading edge contouring. Additionally, scraping tools are difficult to manipulate and fatiguing to the operator. Free standing motor-driven abrasive wheels and belts have also been used for shaping the leading edges of the blades. Application of such devices requires significant judgement on the part of the operator in maintaining the edge in proper engagement with the abrasive and further requires, even with experienced operators, continuous inspection and extensive rework. In other prior art devices blades are fixtured and translated relative to an abrasive element. These devices have proven to be either costly or limited to shaping blades of relatively simple geometry because translation of not only the blade but also the fixture is required. None of these prior art devices has proven to be satisfactory for inexpensive, efficient, consistent and precise shaping or reshaping of the leading edge of turbomachine blades to a desired profile.